N-i-p-type perovskite solar cells employing n-type graphene transparent conductive electrodes

Despite intensive studies on perovskite solar cells (PSCs) by employing graphene transparent conductive electrodes (GR TCEs), no use of n-type GR as a TCE has been reported for PSCs. It is known to be technologically more easy to prepare p-type GR TCEs than n-type ones because even pristine GR usually exhibits p-type characteristics in air. P-type GR can be employed in p-i-n-type PSCs as a TCE, but not in n-i-p-type ones. In addition, most of the p-i-n-type structures are not suitable for flexible substrates due to the inherent high-temperature annealing process. Here, n-type (Ag nanowires-doped) GR TCEs are first used for n-i-p CH₃NH₃PbI₃ (MAPbI₃) PSCs. With increasing the doping concentration (n_A) of Ag nanowires to 0.3 wt%, the sheet resistance (R_s) and transmittance (T) of the TCE monotonically decrease to ∼52 Ω/sq and ∼90%, respectively. Due to the n_A-dependent trade-off relation between the R_s and the T, the DC conductivity/optical conductivity ratio is the largest (∼62) at n_A = 0.1 wt%, resulting in maximum power conversion efficiencies (PCEs) of 15.80 and 13.45% for the PSCs on rigid and flexible substrates, respectively, indicating PCE enhancements more than 50 and 30% by using the n-type GR TCEs.